1. Field of the Invention
The present invention relates to a thermal printer.
2. Description of the Related Art
As a conventional thermal printer, there is one disclosed in, for example, Patent Document 1.
In the thermal printer disclosed in Patent Document 1 (JP 2000-318260 A), a pressure spring is disposed between a back surface of a thermal head and a lock arm for supporting a platen roller disposed so as to oppose to a printing surface side of the thermal head. Due to a biasing force of the pressure spring, the platen roller and the thermal head come into close contact with each other by a predetermined pressurizing force.
In the thermal printer described in Patent Document 1, in a case where heat sensitive paper is jammed between the platen roller and the thermal head or the like, it is necessary to swing the lock arm to cause the platen roller and the thermal head to be spaced apart from each other. Herein, the lock arm is allowed to swing to cause the platen roller and the thermal head to be spaced apart largely from each other, so the jammed heat sensitive paper can be readily removed. In addition, after the jammed paper is completely removed, due to the biasing force of the pressure spring, the platen roller and the thermal head can be returned to original positions thereof.
According to the thermal printer, the pressure spring is shared as a pressure spring for pressing the platen roller and the thermal head by the predetermined pressurizing force so as to come into close contact with each other and as a pressure spring for restoring the lock arm swinging. Thus, components can be reduced in number and cost can be reduced, which are advantageous.
However, in the thermal printer described in Patent Document 1, because the pressure spring effectively applies its pressurizing force to the thermal head, it is preferable that the pressure spring be disposed on an extended line connecting a contact position of the thermal head and the platen roller and an axial center of the platen roller. Accordingly, a position of the pressure spring is distant from a swing center of the lock arm, which is inconvenient. That is, a stroke of the pressure spring becomes large to secure a sufficient swing range of the lock arm, which is inconvenient.
In the case where the stroke of the pressure spring is large, a space in which the pressure spring having the large stroke and a portion of the lock arm are disposed is necessary to be defined at the back surface side of the thermal head. Thus, there arises a problem in that the back surface side of the thermal head cannot be made compact.